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Sudden Death: A Tale of Cell Suicide at the Cambridge Science Festival

newspaper update; 4/19/2013

The Cambridge Science Festival has multiple events everyday in mid-April. The events can be from engineering to medical science and astronomy to biology. Most of the events’ admissions are free and can be attended by everyone from children to adults. One intriguing event was on Wednesday, April 17th. This was about cell suicide, or how cells kill themselves in a clean and orderly way. The event was lectured by Marshall Thomas, a PhD Candidate at Harvard University, who programs in biological and biomedical sciences.

People who studied Biology know that there are tens of trillions of cells in an average human body and most cells, when exposed to infections or harmful foreign bodies, kill themselves in order to not harm any of the neighboring cells. Cell suicide in scientific terms is called apoptosis. Apoptosis is a program of cell destruction. It is a clean and organized way for a cell to recycle its components. An alternative to apoptosis is necrosis. Necrosis shuts down the cell without recycling any of the cell’s components which is harmful to the cells and the organism. A more common term for necrosis is called gangrene. Inside a multicellular organism’s body, such as a human’s, hundreds of millions to billions of cells per day go through apoptosis. Most cells in the human body go through apoptosis in 4 to 6 hours. The nerve cells are one of the only cells that rarely go through apoptosis and cannot regenerate new ones as fast as liver or skin cells. Cells die in a response to stress, such as sunburn. Another reason why cells die is to prevent cancer by removing old damaged cells.

Living cells are enclosed by a membrane and inside are the organelles that make compartments. In the nucleus of the cell there are DNAs that encode the cell’s blueprints of apoptosis. Pieces of DNA copy, or transcribe, into the messenger RNA (mRNA) and then the mRNA translates into protein. Finally, the proteins inside the cells start the process of apoptosis.

In response to stress, the proteins inside cells recognize the damage in the DNA and attempt to repair it by activating apoptosis. When apoptosis is in order, it is fast and irreversible. The mitochindria in cells control the first step (the “trigger”) in apoptosis. Within the mitochondria, there are cytochrome complexes (cytochrome C) which are heme proteins. Apoptosis proteins create holes in the outer membrane of the mitochondria and release the cytochrome C. Once the cytochrome C’s are out of the mitochondria, they bind with the proteins to make a scaffold. These cytochrome C’s bound proteins now self-assemble into a circular scaffold for a key to lock in, which is where caspase 9 comes into play. The caspase 9 with the newly formed scaffold then starts to create a cascade. This creates caspase 3, which is called “the executioner”. The goal of the phase when the caspase 9 creates many caspase 3’s is to shut down vital functions, break down cell components, and call in the cleanup crew. Caspase 3 cuts out spherical blebs of cell components and binds them in a membrane to make sure they do not leak during apoptosis. When the cleanup crew is called the phosphyatidylserine, or the “eat me” signal, is turned on. The “eat me” signal makes sure that the cell components are recycled instead of being left to die like necrosis. That is how apoptosis works in cells.

This lecture and many others were brought to you by Science in the News (SITN) and Cambridge Science Festival.

To learn more visit https://sitn.hms.harvard.edu/sitn-seminars/ and http://cambridgesciencefestival.org/Home.aspx

by Neal Suh

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